Orthogonal frequency-division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA) wireless communication systems, such as those compliant with the Institute of Electrical and Electronics Engineers (IEEE) 802.16 family of standards, typically use a network of base stations to communicate with wireless devices (i.e., mobile stations) registered for services in the systems based on the orthogonality of frequencies of multiple subcarriers and can be implemented to achieve a number of technical advantages for wideband wireless communications, such as resistance to multipath fading and interference. Each base station (BS) emits and receives radio frequency (RF) signals that convey data to and from the mobile stations (MS).
One example of a communication system based on an orthogonal multiplexing scheme is a WiMAX system. WiMAX, which stands for the Worldwide Interoperability for Microwave Access, is a standards-based broadband wireless technology that provides high-throughput broadband connections over long distances. The WiMAX standards define a sleep mode during which a mobile station (MS) may power down components in an effort to conserve power. In the sleep mode, the MS may power up components to monitor page messages in recurring MS Paging Listening (“listening”) intervals, while powering down components in MS Paging Unavailable (“sleep”) intervals.
Current versions of the WiMAX standards specify that the sleep mode may be deactivated when a MS starts a handover (HO) operation. HO operations may be used to transfer service provided to an MS from a serving BS to a target BS. To deactivate the sleep mode, the MS may employ a mobile station handover request (MOB_MSHO-REQ) or a handover indication (MOB_HO-IND) message, while the BS may utilize a base station handover request (MOB_BSHO-REQ) or the MOB_HO-IND message.
In some scenarios, attempts to perform HO operations may be hindered. For example, during the HO process, an MS may leave a region covered by the target BS or the signal provided from or to the BS may be obstructed. When the HO to a target BS is hindered, the MS may re-establish service with the serving BS.